Sputter ion pumps operate
a gas within a magnetically confined cold cathode
discharge. The events that combine to enable pumping of gases under vacuum
- Entrapment of electrons in orbit by a magnetic field.
- Ionization of gas by collision with electrons.
- Sputtering of titanium by ion bombardment.
- Titanium gettering of active gases.
- Pumping of heavy noble gases by ion burial.
- Diffusion of hydrogen and helium into titanium.
- Dissociation of complex molecules into simple ones for pumping ease, e.g., CH4 breaks down into C and 2H2. Hydrogen is pumped separately. Carbon is no longer part of the residual gas and resides in solid form.
Burial is the basic means of pumping heavy noble gases. Argon ions
neutralized via glancing collisions with a sputter cathode
impact the pump wall and are coated with sputtered titanium. Triode
pumps are specially designed to maximize the kind of collisions that produce energetic neutrals.
Argon is permanently pumped on the wall behind the cathode in these pumps. The wall area receives titanium for inert gas burial but, because of a retarding electric field between the cathode and the wall, it is not subjected to ion bombardment and thus gases are not resputtered.